Neurological trauma, dysfunction or disease can leave persons with severe and life threatening motor or sensory disabilities that can compromise the ability to control basic vital functions. Persons with neurological impairments often rely on personal assistants, adaptive equipment and environmental modifications to facilitate their daily activities. Neural prostheses are highly effective methods for restoring function to individuals with neurological deficits by electrically manipulating the peripheral or central nervous systems. By passing small electrical currents through a nerve, neural prostheses can initiate action potentials that eventually trigger the release of chemical neurotransmitters to affect an end organ or another neuron. Techniques exist to selectively activate axons of any size or location within a nerve or fascicle, making it possible to preferentially target small sensory fibers or duplicate natural motor unit recruitment order to minimize fatigue and grade the strength of a stimulated muscular contraction. In addition to exciting the nervous system, the proper current waveform and configuration of electrodes can block nerve conduction and inhibit action potential transmission. Thus, in principle any end organ normally under neural control is a candidate for neural prosthetic control.
Neural prosthetic devices that electrically stimulate paralyzed muscles provide functional enhancements for individuals with spinal cord injury and stroke such as standing and stepping, reaching and grasping, and bladder and bowel function. Current implanted neural prosthetic systems utilize considerable external powering and signal processing, and each system is tailored to the specific application for which it was intended. The need to design a customized implant system for each application severely limits progress in the field and delays introduction of new technology to the end user.
Generally, neural prostheses consists of both external and implanted components. External components consist of sensing apparatus, signal processing, and transmission to an internal implanted component. The internal component receives the externally transmitted signal and generates appropriate stimuli in response to the signal. The internal components might also include sensors, which measure some internal variable and transmit the signal to the external apparatus for processing.
Implanted neural prostheses have been successfully applied to the sensory (e.g., cochlear and visual prostheses) and motor (i.e. hand grasp) systems, as well as to the viscera (e.g., micturition, defecation) and central nervous system (e.g., deep brain stimulation).
In further advancements of neural prostheses, a number of sensors and actuators have been combined into networks that cooperate to extend a neural prosthesis over an area of the body, with nodes of the network operating under control of a central controller. Such networks are described, for example, in U.S. Pat. No. 5,167,229 to Peckham, et al.
It is clear that neural prosthetic approaches can provide both therapeutic and functional benefits to individuals with impairments due to neurological injury or disorder. However, as a significant disadvantage prior neural prostheses typically provide only crude networking capability and limited, if any, programmability at nodes within the prosthetic network. Despite the promise of neural prostheses, there remains a need for a an architecture that is sufficiently open and flexible to permit the implementation of complex and varying prosthetic functions, and to invite the design of a wide range of sensors and actuators for use therewith.